Thick-billed Weaver Amblyospiza albifrons

Discovery

Thick-billed Weaver figure from Swainson 1838

Thick-billed Weaver figure from Smith 1840

Thick-billed Weaver figure from Smith 1840

Thick-billed Weaver distribution, type locality circled

Introduction

The Thick-billed Weaver was formally described by Nicholas Aylward Vigors, an Irish zoologist and politician. Vigors was a co-founder of the Zoological Society of London in 1826, and its first secretary until 1833.

The Thick-billed Weaver specimen was presented to the Zoological Society of London by Henry Ellis, an English librarian at the British Museum. It is not known from whom Ellis obtained these specimens.

Vigors described nine new species from the Ellis collection and the specimens were all believed to have come from Algoa Bay and surroundings in the Eastern Cape. Two species, however, the Purple-crested Turaco Tauraco porphyreolophus and the Spotted Thrush Zoothera guttata, have their southern limits further north in the Transkei (and may have come from Durban), but the rest of the specimens probably did originate from the Algoa Bay area.

The first illustration of a Thick-billed Weaver is in Swainson (1838), showing a line drawing of the very heavy bill of a male. A few years after this species was first described, Andrew Smith found this species in 2 places: in the Eastern Cape forests (probably not too far from Grahamstown, as Smith was based there in his early years in South Africa) and around Durban (Port Natal) in 1832. Smith commisioned the first colour illustrations of the The Thick-billed Weaver - these were published as 2 plates in Smith (1840), and painted by George Henry Ford.

1. Basic biology

Thick-billed Weaver, head of male

Thick-billed Weaver, female

Identification.
The Thick-billed Weaver Amblyospiza albifrons is in a monotypic genus (only one species in the genus), namely Amblyospiza, this name meaning "blunt, finch", referring to its amazingly heavy bill. The male has a black bill, white forehead (photo left) and conspicuous white patches in its wings; the rest of its plumage varies racially, from chestnut to black. The sexes are dissimilar, and the female has a yellow bill, brown upperparts, and underparts white heavily striped with sepia. The juvenile resembles the female, but the bill is yellowish; immature males need 2 years to attain adult plumage.

Distribution.
The Thick-billed Weaver is widespread in sub-Saharan Africa and has five subspecies.
A. a. albifrons is found in southern Africa to central Mozambique (red on map).
A. a. capitalba occurs in West Africa from Sierra Leone to Angola and DR Congo (light green); the male has the white forehead patch extending onto the crown, the rest of the head is light rufous-brown contrasting with the dark chocolate-brown upperparts, and with grey-brown belly.
A. a. melanota is found from southern Sudan south to Burundi and NW Tanzania (purple); the male has a small white forehead patch, and dark brown head contrasting with the black upperparts.
A. a. montana occurs from the interior of Kenya south to Botswana (Okavango Basin) and Zimbabwe (yellow); the male is very dark, nearly black.
A. a. unicolor occurs along the coast from Somalia to Tanzania, including Zanzibar and Pemba I (brown); the male is smaller, has some brown wash on the head, but no obvious colour contrast.

This species is expanding its range, especially in the provinces around Gauteng in South Africa (see here).

Habitat.
The Thick-billed Weaver inhabits wetlands when breeding and forest edges when not breeding, and shows some local movements. It is a fairly common species locally.

Food.
The Thick-billed Weaver feeds on insects (including termites), berries and fruit, and hard-shelled seeds; also sunflower seeds. An adult in Kenya ate a small frog, and aquatic snails have been recorded in its diet.

Female Thick-billed Weaver investigatinga new nest

Breeding.
The nest of the Thick-billed Weaver is distinctive. It is compact, woven with thin strips of reeds, slung between upright stems of reeds. The nest is globe-shaped with a side entrance near the top. The fine material used lets a nest look neat, but actually the weave is very primitive.

Initially the entrance is large, and reduced to a narrow opening if used for breeding. Colonies may be small with one male, or larger with several males, in a reed patch. This species is polygynous, the male attempting to attract several females.

The mean clutch size 3 eggs, and the eggs are white to pink, spotted with red, purple and brown. Incubation is by the female, with long incubation spells of 33 minutes (and 12 minutes off the nest). The chicks are fed by the female (by regurgitation), and sometimes the male also feeds. Nest predators include the White-browed Coucal Centropus superciliosus, House Crow Corvus splendens, and Nile monitor Varanus niloticus.

Old nests may be taken over by climbing mice, and used for breeding by the Zebra Waxbill Amandava subflava or Brown Firefinch Lagonosticta nitidula.

2. Breeding facts

Pair bondPolygynous, male with up to six females, three nesting simultmeously on teritory; also single nests and apparently monogamous pairs in areas of low densityBreeding seasonMay-Nov in Cameroon, Jul-Oct in Central African Republic, Nov in Sudan, and May-Jun and Aug-Sept in Ethiopia; in DRCongo, Jan-Mar in Katanga, Jun-Nov in Ituri and Jan in Itombwe; all months except Nov-Dec (peak Apr-Jun) in Uganda; in Kenya Apr-Oct on coast and all months except Sept-Oct (peak Mar-Jun) inland; Mar-Apr in Rwanda, Dec-Feb and Apr-May in Tanzania, and Dec-Mar in Mozambique, Angola, Zambia and Malawi; Jan-Feb and Apr in Botswana, and Nov-Mar in Zimbabwe; in South Africa, Nov-Mar inland and Sept-Mar in coastal regionsNest siteattached, 1-3 m above ground or water, to bulrushes , papyrus (Cyperus papyrus) or reeds (Phragmites) and sedges, usually over water, also in tall elephant grass (Pennisetum purpureum)Nest buildingbuilt by male, female lining cupColony sizeOften in small colonies; more than 100 nests in one South African colonyClutch sizemean 3 eggs (Malawi, South Africa)Egg colourwhite to pink, spotted with red, purple and brownEgg sizeaverage size of 165 in S Africa 23.6 x 16.2 mmIncubationby female, in mean spells of 33 minutes (mean 12.5 minutes off nest), period 14-16 daysChicks and nestling periodchicks fed by female (by regugitation), occasionally by male, nestling period 18-20 days